P-n junction based photovoltaic cells are commonly used as solar cells. Generally, p-n junction based photovoltaic cells include a layer of an n-type semiconductor in direct contact with a layer of a p-type semiconductor. By way of background, when a p-type semiconductor is positioned in intimate contact with an n-type semiconductor a diffusion of electrons occurs from the region of high electron concentration (the n-type side of the junction) into the region of low electron concentration (the p-type side of the junction). However, the diffusion of charge carriers (electrons) does not happen indefinitely, as an opposing electric field is created by this charge imbalance. The electric field established across the p-n junction induces a separation of charge carriers that are created as result of photon absorption.
Chalcogenide (both single and mixed) semiconductors have optical band gaps well within the terrestrial solar spectrum, and hence, can be used as photon absorbers in thin film based photovoltaic cells, such as solar cells, to generate electron-hole pairs and convert light energy to usable electrical energy. More specifically, semiconducting chalcogenide films are typically used as the absorber layers in such devices. A chalcogenide is a chemical compound consisting of at least one chalcogen ion (group 16 (VIA) elements in the periodic table, e.g., sulfur (S), selenium (Se), and tellurium (Te)) and at least one more electropositive element. As those of skill in the art will appreciate, references to chalcogenides are generally made in reference to sulfides, selenides, and tellurides. Thin film based solar cell devices may utilize these chalcogenide semiconductor materials as the absorber layer(s) as is or, alternately, in the form of an alloy with other elements or even compounds such as oxides, nitrides and carbides, among others.
Numerous deposition methods have been proposed for the preparation of the photovoltaic absorber layers, among other thin films, and their precursors. By way of example, such photovoltaic absorbers include CdTe, CuInS2, Cu(InGa)Se2, and CuInSe2, among others, while their precursors include, by way of example, CuIn, CuGaIn, and In2S3/Cu, among others. Conventionally, in the case of precursors, the constituent metallic components are first deposited onto a substrate and then the final compound, a chalcogenide having chalcopyrite phase, is obtained through thermo-chemical processing.